1. Field of the Invention
The present invention relates to a process of preparing commercial quantities of glucose from sucrose, and a reactor for practicing same. In particular, the present invention relates to a process for preparing glucose from sucrose by contacting sucrose with a .beta.-2,1-fructosyltransferase and a .beta.-2,6-fructosyltransferase, followed by isolating glucose and a branched fructan, thereby enhancing production efficiencies.
2. Description of the Background
Glucose is a saccharide that is found throughout nature, either as a monosaccharide or incorporated into polysaccharides. Glucose is used clinically as a fluid and nutrient replenisher, as a carbon source in the culturing of microorganisms, and is widely used as a food additive.
Glucose has been prepared commercially from starch (Dean, Gottfried, Advan. Carbohyd. Chem. 5, 127 (1950) and by acid hydrolysis of sucrose. In spite of the availability of the starting materials for preparing glucose the cost of this material remains high, relative to the cost of the starting materials. Accordingly, commercial syntheses of glucose can be improved.
Fructans are found throughout nature (Science and Technology of Fructans, 1993 ed. M. Suzuki and N.J. Chatterton, CRC Press, Inc.). In plants, there are four fructans described 1) inulin, a 2,1- linked fructan found mainly in dicots, such as Jerusalem artichokes and chicory roots; 2) levan or phlein, a 2,6-linked fructan found in some monocots such as timothy; 3) a 2,1- and 2,6- branched fructan found in monocots such as barley, blue agave and wheat; and 4) a fructan of the neoseries, a 2,1-and 2,6-linked fructose on the glucose. The glucose is internal in these molecules, instead of terminal. Fructose residues are then linked 2,1-and 2,6-to both terminal fructose, creating a complex structure (asparagus). Many plants produce more than one of these fructans.
In yeast and fungi, 2,1-linked fructans have been reported.
In bacteria, two fructans have been described 1) an inulin 2,1-fructan from Streptococcus mutans and 2) a levan 2,6-linlked fructan has been described from Bacillus subtilis, Zymomonas mobilis, and many others.
Inulins are comprised of .beta.-2,1-linked fructose chains, linked to an .alpha. D-glucoside; they have a linear structure and typically comprise many .beta.-O-fruc tofuranose units. The average chain length and molecular weight distribution will depend on both the plant species, the growth phase, and the preparation method. Average chain lengths of 10 to 25 are common, in which case the individual units have about 9 to 24 fructose units.
Branched inulins have been reported, which comprise a linear chain of .beta.-2,1-linked fructose chains, linked to an .alpha. D-glucoside, having branched thereon, .beta.-2,6 fructose units. Such a branched inulin material has been reported having been isolated from the sap of the blue agave plant (G.O Aspinall and P.C. Das Gupta Proceeding of the Chemical Society 1959 718-722 and M. N. Satyanarayana Indian J. of Biochem and Biophys. (1976) 13:408-412) and from barley leaves (Simmen et al., Plant Physiol. (1993) 101:459-468).
The properties of an inulin may vary depending on the chain length and the degree of branching. Compositions comprising linear short chain inulins having a degree of polymerization of about 3 to 7 fructose units have been used as reduced calorie sugar substitutes (DE 4,003,140). Longer chain inulins have been uses is fat mimetics and branched fructans may be used as both.
Coussement et al. U.S. Pat. No. 5,659,028 discloses branched fructo-oligosaccharides consisting of a chain which comprises mainly fructose units and has a preferred chain length of 2 to 15 units, on which are fixed one or more side chains mainly composed of fructose units.
In the area of glucose production, Nagle et al. U.S. Pat. No. 4,637,835 report the preparation of glucose and other saccharides from an .alpha.-cellulose using a calciurm chloride catalyst and hydrogen ions.
Miyawaki et al. U.S. Pat. No. 5,524,075 report the production of high purity glucose by saccharifying liquefied starch with an enzyme.
Venkatasubramanian et al. U.S. Pat. No. 4,299,677 report the direct separation of fructose and glucose from a mixture of glucose and fructose by ion exKchange membranes.
Harada et al. U.S. Pat. No. 5,169,679 report the use of fructans composed mainly of .beta.-2,1 bonds having a molecular weight of from 2,000 to 20,000,000 as food additives such as, for example, bulking agents or fat substitutes, for producing low calorie foods.
Kurz et al. U.S. Pat. No. 5,478,732 report a method for obtaining intermediate-chain inulins (e.g., a degree of polymerization of 10-12) by treatment of crude inulin suspensions with a hydrolase enzyme. During the enzymatic treatment, short-chain components are degraded to mono- and disaccharides while long-chain inulins are separated off, then converted to a dry form.
Adachi et al. report in U.S. Pat. No. 4,681,771 that when sucrose (G-F) is contacted with an enzyme having fructose transferring activity (hereinafter referred to as a fructosyltransferase), a low caloric, low-cariogenic sweetener composition is obtained which comprises glucose, sucrose, the trisaccharide (GF.sub.2), the tetrasaccharide (GF.sub.3) as well as minor amounts of fructose, pentasaccharide (GF.sub.4) and hexasaccharide (GF.sub.5). The amount of higher linear inulins drops off dramatically, the majority fraction being inulin GF.sub.2-3.
Kono et al. U.S. Pat. No. 5,314,810 report that the half-life of an immobilized fructosyltransferase used in the reaction with sucrose can be improved by support on a granular carrier such as chitosan derivative or an anion exchange resin. Such a supported enzyme is reported to allow for the industrial production of a low cariogenic sweetener composition.
Heady U.S. Pat. No. 4,317,880 reports the production of novel fructose polymers and high fructose syrups from sucrose by the combined action of a fructosyltransferase enzyme and a glucose isomerase enzyme preparation.
A method of producing glucose and/or fructose irom sucrose is reported by Catani et al. in co-pending U.S. application Ser. No. 09/019,709 filed on Feb. 6, 1998.
Present methods for preparation of glucose from sucrose however, have suffered from poor efficiency, such that the production of commercial quantities of glucose can be improved.
In addition, there remains a need for processes for preparing commercial quantities of polysaccharides such as linear and branched inulins.